11yr old son pooping his pants

I have an 11yr old boy that still poops his pants. He doesn't seem to care if he is dirty or if anyone can smell him.
He even goes so far with it when i tell him to go clean himself then take a bath I go in to check on him and he is in the tub with poop floating around in it, needless to say he now takes showers in the times he needs to do this.
We have taken him to the Dr. with no physical results as to why he is doing this, he knows he is and when he does.
When you get a nose full of him and you know he is dirty and you ask him "Are you dirty again"? He will give one of two responses. I don't know, or he will blatantly just tell you no.
What gets me is that it does not matter what form of discipline you use, or what you take away from him it is never extreme enough to get him to stop. I have even went so far as to tell him that when he was swimming around in it in the tub that it could make him sick enough that he could die from it and it still happens.
Now what gets me the most is that there are times of clarity when we have taken something from him and he does not do this, I think the longest time was he went two weeks without an episode but slowly fell back into doing it again so that tells me that he can stop if he wants to but willingly continues to dirty himself anywhere and everywhere no matter what and has no more concern about than sneezing or coughing.
Any ideas that maybe helpful will be greatly appreciated.

[Kevin Kennedy, Ph.D.]

I'm going to assume that your son's encopresis is not the only problem he displays. The encopresis is likely accompanied by other issues as well and in any case he should be evaluated by a medtal health clinician. Ask his pediatrician for guidance about how you should go about this.

As a minor aside, when you know he has soiled himself, why do you continue to ask him if he has done so.You already know the amswer to that question.  There is no point in asking that question. Simply tell him to go clean himself up.